It's heavy on enforcement, granting $2.5 billion to states over five years, of which 60 percent would go to enforcement, such as incarceration, and only 40 percent for prevention programs such as drug treatment.

To get the money, states would have to meet tough conditions, prosecuting 14-year-olds as adults for the worst offenses, testing juveniles for drugs upon arrest for violent crimes, fingerprinting all juveniles arrested for felonies, and allowing states to house juveniles in adult jails before trial.

Critics say the Republican bill is too harsh.

"This is one of the few crime bills I've ever seen that's opposed by the National Governors' Association, the district attorneys, the police chiefs, the Children's Defense Fund, the NAACP and most of us who practice in the business," said Wallace Mlyniec of the Georgetown University Law Center. "Now that's a rare event."

Democrats are also talking tough, proposing to build more prisons for juveniles, and to keep them there longer, up to age 25, rather than releasing them at 21.

Would tougher laws have prevented the Arkansas shootings?

Even the Republican bill's sponsor says no.

"I don't think there's anything that would have seriously impacted this case," said Sessions. "I've not seen anything in my 17 years as a prosecutor to compare with this."

So tragedy may lead to irony: Congress moved to pass a law by a violent event the law could not have prevented.